1. Field of the Invention
The present invention relates to the field of semiconductor processing and more particularly to a removal chemistry for selectively etching metal hard masks.
2. Discussion of Related Art
Photoresist masks are commonly used in the semiconductor industry to pattern materials such as semiconductors or dielectrics. In one application, photoresist masks are used in a dual damascene process to form interconnects in the backend metallization of a semiconductor device. The dual damascene process involves forming a photoresist mask on a dielectric layer overlying a metal conductor layer, such as a copper layer. The dielectric layer is then etched according to the photoresist mask to form a via and/or trench that expose the metal conductor layer. The via and trench, commonly known as dual damascene structure, are usually defined using two lithography steps. The photoresist mask is then removed from the dielectric layer before a conductive material is deposited into the via and/or trench to form an interconnect.
With the decreasing size of semiconductor devices, it becomes more difficult to achieve the critical dimensions for vias and trenches. Thus, metal hard masks are used to provide better profile control of vias and trenches. The metal hard masks can be made of titanium (Ti) or titanium nitride (TiN), and are removed by a wet etching process after forming the via and/or trench of the dual damasene structure. It is essential that the wet etching process uses a removal chemistry that effectively removes the metal hard mask without affecting the underlying metal conductor layer and dielectric material. In other words, the removal chemistry is required to be highly selective to the metal conductor layer and dielectric layer.